Method of curing elastomers with thiocarbamyl thiomethyl sulfides

ABSTRACT

WHERE R1 and R3 are alkyl or aryl, R2 and R4 are alkyl with the understanding that R1 and R2 and R3 and R4 may form a ring, and where x is an integer of from 2 to 6. These new compositions are useful as accelerators for the sulfur vulcanization of unsaturated elastomers and may be used as vulcanizing agents.   Novel compounds having the structure

United States Patent mi Albert, deceased [4 1 Apr. 3, 1973 [54] METHODOF CURING ELASTOMERS [56] References Cited gggggfigg UNITED STATESPATENTS [75] I Inventor: Harry Elmer Albert, deceased late 3,579,5165/1971 Albert ..260/249B iig i 5 9 by Dorothy Primary Examiner-James A.Seidleck e exec Assistant Examiner-C. A. Henderson, Jr. [73] Assignee:Pennwalt Corporation, Philadelphia, Attorney-Robert G. Danehower v Pa.22 Filed: Aug. 5, 1970 [57] APSTRACT [211' pp No 61 467 Novel compoundshaving the structure Related US. Application Data E s z 2 E [62]Division of Set. No. 781,691, Nov. 29, 1968, Pat. No. R x

52 "260 795 B where R and R are alkyl or aryl, R, and R are alkyl E51}rm. Ci. ..'.ff....7fi?%,32 with the understanding M R1 and R2 and R3 andR4 [58] Field of searchuz6ol79j B 246 8,455 A 792 may form a ring, andwhere x is an integer of from 2 I 260/784, 793 to 6. These newcompositions are useful as accelerators for the sulfur vulcanization ofunsaturated elastomers and may be used as vulcanizing agents.

6 Claims, No Drawings METHOD OF CURING ELASTOMERS WITH TIIIOCARBAMYLTHIOMETHYL SULFIDES This application is a division of Ser. No. 781,691,filed Nov. 29,1968, now US. Pat. No. 3,579,516.

This invention provides new compositions of matter which are very activeaccelerators for the sulfur vulcanization of unsaturated elastomers suchas styrenebutadiene rubbers, natural rubber, and the recently developedelastomeric terpolymers of ethylene, propylene, and a nonconjugateddiene which terpolymers are known as EPDM elastomers and are reported atpage 15 of Chemical Engineering News, Jan. 23, 1967. These EPDMelastomers require a very high rate of cure for the proper degree ofvulcanization and the compounds of this invention provide this necessarycure rate. The compounds of the invention are also very active asvulcanizing agents, and in many cases can be used to replace thecombination of sulfur and accelerator for curing unsaturated elastomers.

The compounds of the invention have the following structure:

R1 S S R; N( SCH2-S CHzSH-N where R and R are alkyl or aryl, R, and Rare alkyl with the understanding that R and R, and R, and R may form aring, and where x is an integer of from 2 to 6. Preferred compounds arethose where the R groups are alkyl of one to six carbon atoms and alsowhere R and R, and R and R form rings such as oxydiethylene, andpentamethylene.

The new compounds of this invention are readily derived in good yieldfrom commercially available inexpensive raw materials. The reactionsinvolved proceed rapidly at ordinary temperatures and are only mildlyexothermic so that in most cases the preparations can be carried outwithout the added expense and inconvenience of using a solvent. Althougha number of procedures can be used for the synthesis of these newcompounds, the best procedure is to use a secondary amine, hydrogensulfide, sulfur, paraformaldehyde and carbon disulfide. For example, thepreparation of bis(N,N-dimethylthiocarbamylthiomethyl)disu lfide beaccomplished by the following sequence of reactions (Me is used tosymbolize the methyl group and Et symbolizes the ethyl group):

(II) (CI-LO), Me,NCI-I,SSCl-I,N Me,(lll) 2l-I,O

Water in small amounts is a convenient solvent for Steps (I) and (2) toprevent excessive solid separation. For Steps (3) and (4).it is adiluent, since'the products of these reactions are not soluble in water.This method has the advantage of using reactions which proceed rapidlyat room temperature and has the added advantage of avoiding the use ofinorganic salts. The intermediates can be separated and purified ifdesired. This reaction sequence permits the isolation of crude productby simply removing, by evaporation or other means, the small amount ofwater present at the end of the reactions. In Reaction 3, aqueousformaldehyde can be used instead of paraformaldehyde.

An alternative to the above procedure involves the following reactionsfor the preparation of compound (II) above A'Ei's'ise'd to symbolize theacetyl group):

(5) Me,NH HOAc "19 Me,NH,OAc (IV) (6) Na,S +8 "19 Na,S, (V)

+ 2Na0 Ace Paraformaldehyde can be used as a substitute for aqueousformaldehyde in Reaction (8). In Reaction (l0), non-oxidizing acidsother than acetic acid may also be employed.

The following examples illustrate the procedures employed for obtainingthese compounds:

EXAMPLE 1 Bis(N,N-dimethylthiocarbamylthiomethyl) Disulfide To 325 g.(4.3 moles) of 60 percentdimethylamine in a three liter 3-neck flask,provided with a thermometer, motor-driven stirrer, reflux condenser anda gas inlet tube, 80.5 g. (2.36'moles) of hydrogen sulfide was addedduring stirring and cooling at room temperature. Addition of 69.0 g.(2.15 g. atoms) of powdered sulfur to the solution obtained in the abovereaction was followed by a rapid reaction giving a clear dark redsolution. Paraformaldehyde (136 g. 4.3 moles CH,0) was thenaddedinportions. It readilyreacted, the dark red homogeneous solution changingto a greenish 2-phase reaction mixture. Addition of 360 g. (4.75 moles)of carbon disulfide was rapidly carried out and the reaction mixture wasstirred 4 hours at room temperature. If desired, this step in thereaction sequence can be shortened by use of mild heating, for exampleat 45 to 50C. The organic layer started to solidify so 300 ml. of

benzene was added to facilitate stirring. After overnight stirring, 600ml. of hexane was added and the solid product was filtered. The creamcolored dry solid weighed 500 g., m.p. 96 106C. An additional 32 g. ofproduct was isolated from the organic layer of the fil trate. A portionof the product was purified by recrystallization from chloroform-hexane.

Analysis: %C=29.28, %I-I=S.l8,

%S=57.52, M.W.=389 Calcd: %C=28.88, %H=4.85, %N=8.42, %S=57.85,

M.W.=332.6 Infrared absorption was consistent with the assignedstructure.

(VII) EXAMPLE 2 Bis(N,N-dimethylthiocarbamylthiomethyl) Trisulfide In a3-neck flask, provided with a motor-driven stirrer, reflux condenser, athermometer and an addition funnel 112.5 g. (1 mole) of 40 percentdimethylamine was reacted with 81.0 g. (1 mole) of 37 percent aqueousformaldehyde, the latter being added slowly through the addition funnelduring stirring and cooling. Then 76 g. (1 mole) of carbon disulfide wasadded under the same conditions. A mixture of 120 g. (0.5 mole) ofNa,S'9H O, 100 ml of water and 32 g. (1

mole) of powdered sulfur was heated at 60C. until all i the sulfurdissolved and a clear red solution was obtained. This was cooled andadded to the main reaction been prepared are summarized in Table I whichfollows:

TABLE 1.BIS(THIOCARBAMYL'IHIOMETHYL) POLYSULFIDES React ants (in orderof Compound Structure additi n) Product Analysis Example 3. Bis(N,N-MCzNCSCH2S-S 112.5 g. (1 mole) 40% 158 g. waxy brown Percent: C=23 84;

dimethylthiocarbamylthiodimethylamine. solid, M.P. 5387 C. H =4.45;=7.99; methyl tetrasulfide. S S =63.04.

MenNh3S--CH:SS

81 g. (1 mole) 37% formalde- Structure consistent enable 4. Bis(N,N-

dimethylthlocarbamylthiomethyl)pentasulfide.

Example B. Bis(N, N-

diethylthiocarbamylthiomethyl) dlsulfide.

Example 6. 1315(N. N-(liothylthiocarbamylthlomothyl) trisulfide.

S l I hyde, 76 g. (1 mole) CS;; 217 g. (0.5 mole) 40% sodiumtetrasulfide;

60 g. (1 mole) acetic acid.

' A. 112.5 in mole) 4e.

dlmethylamine, 81 g. (1 mole) 37% CHzO; 76 g. (1 mole) CS2.

B. 120 g.- (0.5 mole) NazS.

9 H; 64 g. (2 g. atoms) powdered sulfur. B added to A, then added 60 g.

(1 mole) acetic acid.

'7 5.126365 mole) NaTS ET H; 16 g. (0.5 g. atom) powdered sulfur.

168.5 g. very viscous brown 011 becoming a semi-solid on standing.

' 136.5 'gTEEEni bFF m liquid.

B. 73 g. (1 mole) diethylaminc amine; 81 g. (1 mole) 37% formaldehyde;76 g. (1 mole) CS1. A added to B, then added g. (1 mole) acetic acid.

118 g. (0.5 mole) N, N (dithiodimethylene) bis (di- 166.2 g. ambercolored liquid.

ethylarnine) (prepared from EtgNH, HES, S and paraformaldehyde). 91 g.(1.2 moles) CS2.

35.4 g. (0.15 mole) N, N-(dithiodimethyiene) bis(di cthylemine); 4.8 g.(0.15 g. atom) powdered sulfur.

42.7 1:. dark yellow liquid.

22.8 g. (0.3 mole) CS with infrared absorption; Calcd. Percent: C=24.21; H=4.07; N=7.06; S=64.66.

Percent: 21,6 H=

Structure consistent with infrared absorption; Calcd.: Percent:

Structure consistent with infrared absorption; Calcd. percent: C =37.10;I-I=6.23; N=7.20; S =49.5.

Percent 8 44.60.

Percent: C=34.21; H=

5.95; N=7.04; S= 52.80; (by difference).

Structure consistent with infrared absorption; Calcrl. (percent):

B. 120 g. (0.5 mole) Na S- 9 H20 16 g. (0.6 5. atom) powdered sulfur.

B added to A then added 60 g. (1 mole) acetic acid.

Structure consistent with infrared absorption: Calcd. (percent): 0=43.2; H=7.25; N=6.3U; S =43.26.

TABLE I.BIS(THIOOA RBAMYLTIIIOMETIIYL) POLYSULFIDES Qontinued Rcactants(in order of Compound Structure addition) Product Analysis Example 8A.Bis(N,N-di-n- S A. 129 g. (1 mole) di-n- 187 g. brown mushy Crude;percent: C=

butylamine; 81 g. (1 mole) 37% CHzO; 76 g. (1 mole) B. 120 g. (0.5 mole)NazS- 9 H; 16 g. (0.6 g. atom) powdered sulfur.

B added to A, then added 60 g. (1 mole) acetic acid.

solid. Recrystallized roduct a white solid M.P. 52-54" C.

Calcd. (percent): C=

Purified product analy- .sis; percent; C=48.12

Structure consistent with infrared absorption.

butylthiocarbamylthio- Example 9. Bis(N,N-oxydicthylenethiocarbamyithiomethyl) disulfide.

258 g. (2 moles) di-n-butylamine; g. (1.03 moles) Has; 32 g. (1 g. atom)powdered sulfur (excess H28 removed with N2).

166 g. (2.05 moles) 37% 01120; 159.6 g. (2.1 miles) CS2.

g g 5 m .5 g. atom) powdered lfur.

B added to A, then added 60 g. (1 mole) acetic acid.

g. (1 mole) morpholine; (1 mol GHzO' (1 mole) CS2. 13. 120 g.

ole) NazS :9 H20; 16 g.

353.5 g. brown oil (solidiified in refrigerator). Recrystallized producta white solid, M.P. 5153 0.

Mixed M.P. with product from Example 8A (M.P. 52-54 0.) gave nodepression.-

Frorn half of crude product (176 g. of oil) 58 g. White powder obtainedby CS treatment MP. 95- 113 C. recrystallized M.P. 121123 C.

retrograde;-

percent: 0 =33.61; H=4.73; S =47.50; N=6.59; 0 =7.57 (by difference)Structure consistent with infrared absorption; Oalcd. percentO=34.55;H=4.84; S=46.20; N=6.72;

Bis(N,N-di-n-hexylth iocarbamylthiomethyl), Disulthiocarbamylthiomethyl)dergone storage at room temperature forperiodszclose to a year with noapparent-change. However, someof the higher polysulfideshavesometendency todecompose slowly in standing with the e'volution' of H28. Ithas been found that the storage stability of such compounds can beimproved greatly by the addition of zinc oxide. For example,bis(dimethylthiocarbamylthiomethyl) vtetrasulfide containing 5 percentzinc oxide (based on organic tetrasulfide) is stable on prolongedstorage at room temperature, but an unstabilized sample gave aslightamount of H 8 evolution after about 3 weeks at roomtemperature'For stabilization of liquids by zinc oxide, settling can beavoided by converting to a solid using an inexpensive carrier, such as asynthetic hydrous'calcium -silicate along with thezinc oxide stabilizer.

Additional compounds which come under the scope of this invention arethe following:

Bis(N,N-pentamethylenethiocarbamylthiomethyl) DisulfideBis(N,N-pentamethylenethiocarbamylthiomethyl) TetrasulfideBis(N,N-tetramethylenethiocarbamylthiomethyl) DisulfideBis(N,N-tetramethylenethiocarbamylthiomethyl) TrisulfideBis(N,N-diamylthiocarbamylthiomethyl) Disulfide DisulfideBis(N,N-dibutylthiocarbamylthiomethyl) TrisulfideBis(N,N-diisobutylthiocarbamylthiomethyl) DisulfideBis(N,N-oxydiethylenethiocarbamylthiomethyl) TrisulfideN,N-Dimethylthio'carbamylthiomethyl N',N- DiethylthiocarbamylthiomethylDisulfide I N ,N-Dimethylthiocarbamylthiomethyl N N Diethylthiocarbamylmethyl Trisulfide Bis(thiocarbamylthiomethyl) Disulfide from variousamine mixtures (such as dimethylamine diethylamine dibutylamine)Bis(Thiocarbamylthiomethyl) Trisulfide from various amine mixtures (suchas dimethylamine diethylamine) fBis(N-phenyl-N-methylthiocarbamylthiomethyl) DisulfideBis(N-phenyl-N-ethylthiocarbamylthiomethyl) Disulfide T he .compduiidsofthe inventioii rnay be used with natural rubber and with varioussynthetic elastomers including, as indicated above, thestyrene-butadienerubbers, the acrylonitrile-butadiene rubbers, polychloroprene, and otherelastomers which are vulcanizable with sulfur, such as the numeroussulfur vulcanizable dienes and their copolymers with acrylates and thelike. As alradyfindicated, the compounds also useful for the new EPDMelastomers. These ethylene propylene terpolymers used as a thirdcomonomer unsaturated compounds such as l,4-hex-.

adiene, ethylidene norbomene, methylene norbomene, dicyclopentadiene,and the like. The amount of the compound used will generally be fromabout 0.1 to

about 5 parts per 100 parts of rubber (phr) preferably from about 0.3 to2.0 phr.

Evaluation procedures for the compounds of the invention follow:

Evaluation in Natural Rubber The chemicals to be tested were milled intoa portion I of this masterbatch. The test results are summarized inTable A. These test results show the product of Example l to be veryactive accelerator at 0.5 phr (parts per hundred parts of rubber),giving a much more rapid cure than the stock without added accelerator(the control) and producing very superior physical proper-' ties. Thetensile strength values obtained were significantly better than thosegiven by tetramethylthiuram disulfide, a widely used commercialaccelerator.

TABLE A Evaluation of Bis(dimethylthiocarbarnylthiomethyl) Disulfide asan Accelerator in Natural Rubber.

Control (no accelerator) Cure in minutes at 298F. 300% modulus Tensilestrength Elongation 10 (no cure) (no cure) (no cure) 20 150 350 500 40175 600 600 0.5 PHR Bis(dimethylthiocarbamylthiometh l) Disulfide(Example 3 Cure in minutes at 298F. 300% modulus Tensile strengthElongation 10 400 3350 700 20 375 3 125 710 40 300 3000 730 0.5 PHRTetramethylthiuram Disulfide (Methyl Thiram) Cure in minutes at 298F.300% modulus Tensile strength Elongation 10 450 2675 600 20 400 2675 65040 a 350 2400 670 B Evaluation in SBR Test Compound SBR 1500 100.0 HAFBlack 50.0 Zinc oxide 5.0 Stearic acid 3.0 Polymeric saturated petroleum10.0 BXQ 'EMQBQ EKQQEQ C.P. Hall Co.) Blackbird sulfur 2.0 170.0

The chemicals to be evaluated were milled into portrons of thismasterbatch. The results are summarized in Table B. These data show theproducts of Examples 5 and 8 to be very active accelerators for thesulfur vulcanization of SBR giving excellent physical properties,' andboth are considerably more active than 2,2 dithiobisbenzothiazole,a'commercial accelerator widely used in SBR. Increasing the rate of cureby increased accelerator concentration is illustrated with the productof Example 8. With the SBR masterbatch alone (control no addedaccelerator but containing sulfur), no measurable tensile propertieswere obtained ylthiomethyl) Pol sulfides as accelerator in SB 0.5 PHRBis(N,N-

dieth lthiocarbamylthiomethyl) Disul de (Example 5) Cure in minutes at298F. 300% modulus Tensile strength Elongation 0.5 and 2.0 PHRBis(N,N-di-nbutylthiocarbamylthiomethyl) Disulfide (Example 8) Cure inminutes at 298F. 300% modulus Tensile Strength Elongation 0.5 phr 2.0phr 0.5 phr 2.0 phr 0.5 phr 2.0 phr 10 200 1875 400 3575 1000 500 20 8752425 2750 3375 850 400 40 1275 2800 3450 3225 700 340 80 1700 2850 35504075 560 320 0.5 and 2.0 PHR 2,2-

Dithiobisbenzothiazole (A commercial Accelerator) Cure in minutes at298F. 300% modulu Tensile Strength Elongation 0.5 phr 2.0 phr o.5 phr2.0 phr 0.5 phr 2.0 phr 10 No cure 200 No cure 400 No curev 950 20Nocure. 800 No cure 2600 No cure 710 40 200 1400 525 3450 800 650 80 5751825 1975 3200 790 500 A control (no additive) did not cure under any ofthe above conditions. C Evaluation in EPDM Test Compound Royalene" 30150.0 "Royalene400 100.0 FEF Black 100.0 Zinc oxide 5.0 Stearic acid 2.0Sulfur 0.5 Z-Mercapto benzothiazole 0.5 258.0

Royalene 301 is a general purpose gum EPDM synthetic rubber, aterpolymer of ethylene, propylene and a non-conjugated diene understoodto be dicyclopentadidne. Royalene 400 15 similar to Royalene 301, but isextended with phr of a naphthenic oil. Thus the test stock used is onthe basis of 100 parts of EPDM gum elastomer. This masterbatch was usedto obtain the results given in Table C. These results show the productof Example 2 to be a very active accelerator, showing significantadvantages in tensile strength and elongation over tetramethylthiuramdisulfide, one of the preferred commercial accelerators now used inEPD'M.

TABLE C Evaluation of Bis(dimethylthiocarbamylthiomethyl) Trisulfide asan accelerator in EPDM synthetic rubber. 4.0 PHRBis(dimethylthiocarbamylthiometh l) Trisulfide (Example Cure in minutesat 320F. 300% modulus Tensile strength Elongation 20 1050 1625 550 301300 1925 450 40 1400 2100 460 60 1475 2075 420 4.0 PHRTetramethylthiuram Disulfide (Methyl Thiram) Cure in minutes at 320F.300% modulus Tensile strength Elongation 20 1125 1625 450 30 1275 1725400 D Evaluation as vulcanizing agents in natural rubber Test stockSmoked sheet 100 MT Black 20 Zinc oxide 1 Z-Mercaptobenzothiazole 1 Testcompounds were milled into this masterbatch to produce rubber stocksfrom which the results of Table D were obtained. The data of this tableshow a high level of activity for the products evaluated. The product ofExample 1 gave'better tensile values than tetramethylthiuram disulfide,a widely used commercial vulcanizing agent and the product of Example 2gave superior modulus values.

TABLE D Evaluation of Bis(dialkylthiocarbamylthiomethyl) Polysulfides asvulcanizing agents for natural rubber 4.0 PHRBis(dimethylthiocarbamylthiomethyl) Disulfide With no additive (control)no measurable tensile properties are obtained.

It is obvious from the above data that the products of this inventionare potentially cheap organic compounds, easily prepared in good yieldsfrom readily available inexpensive starting materials. They areextremely active accelerators for vulcanization of unsatu- 10 ratedelastomers and alsoh ave activity as vulcanizing agents for suchelastomers in the absence of sulfur.

It will be understood that numerous changes and variations may be madefrom the above description of the invention and the examples shownwithout departing from the spirit and scope of the invention.

lclaim:

1. In the process of sulfur vulcanization of diene elastomers theimprovement which comprises incorporating in said elastomers anaccelerating amount of a compound having the formula:

where R and R are alkyl or aryl, R and R are alkyl with theunderstanding that R and R and R and R may form a ring selected from thegroup consisting of alkylene and oxyalkylene, and where x is an integerof from 2 to 6.

2. The process of claim 1 in which the elastomer is natural rubber andin which R,, R R and R are methyl and x is 2. I

3. The process of claim 1 in which the elastomeris styrene-butadiene andin which R,, R R and R are methyl and x is 2.

4. The process of claim 1 in which the elastomer is anethylene-propylene-diene terpolymer and in which R,, R R and R aremethyl and x is 3.

5. In the process of sulfur vulcanization of natural rubber, theimprovement which comprises using as vulcanizing agent a compound havingthe formula:

kylene and oxyalkylene, and where x is an integer of from 2 to 6.

6. The process of claim 5 in which R R R and R are methyl and x is 2.

2. The process of claim 1 in which the elastomer is natural rubber andin which R1, R2, R3, and R4 are methyl and x is
 2. 3. The process ofclaim 1 in which the elastomer is styrene-butadiene and in which R1, R2,R3, and R4 are methyl and x is
 2. 4. The process of claim 1 in which theelastomer is an ethylene-propylene-diene terpolymer and in which R1, R2,R3, and R4 are methyl and x is
 3. 5. In the process of sulfurvulcanization of natural rubber, the improvement which comprises usingas vulcanizing agent a compound having the formula:
 6. The process ofclaim 5 in which R1, R2, R3, and R4 are methyl and x is 2.